mineral

Tumbled gray agate

Microcrystalline quartz (chalcedony), SiO₂

AI-generated identification · may be incorrect

Hardness 6.5–7; gray to brown with subtle curved banding, waxy-to-glassy luster, no visible cleavage, and conchoidal fracture. Specific gravity is about 2.6.

Identified August 16, 2026More mineral →

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Physical properties

Hardness 6.5–7; gray to brown with subtle curved banding, waxy-to-glassy luster, no visible cleavage, and conchoidal fracture. Specific gravity is about 2.6.

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing layered chalcedony over time; most specimens are Paleozoic to Cenozoic in age. The rounded surface indicates human tumbling and polishing.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and lapidary collections; durable agate is also used for small decorative and industrial objects.

Geological facts

Its bands result from changing silica composition, impurities, and fluid conditions during cavity filling. The specimen may also be marketed as gray banded chalcedony if banding is weak.

Field identification & locations

Identify it by its translucent edges, waxy polish, curved bands, and quartz-like hardness; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, Mexico, India, and the United States.